Photoresponsive nanoparticles as light-driven nanoscale actuators

Abstract

Photoresponsive shape memory nanoparticles have a layered smectic ordering and include a photoresponsive moiety selected from the group consisting of azobenzene, stilbene, and spiropyran. Multiple cycles of contraction and extension in these materials can be controlled by UV and visible light. By changing light intensity and exposure time, the magnitude of actuation can be modulated.

What is claimed is: 
     
       1. A method of actuating, the method comprising:
 irradiating an photoresponsive particle actuator with ultraviolet light thereby causing the photoresponsive particle actuator to contract in at least one dimension, and 
 irradiating the photoresponsive particle actuator with visible light thereby causing the photoresponsive particle actuator to expand in the same at least one dimension, 
 wherein the photoresponsive particle actuator has a layered smectic ordering, comprising a photoresponsive moiety selected from the group consisting of azobenzene, stilbene, and spiropyran, 
 wherein said photoresponsive particle actuator is in a condition of having been formed from a surfactant and at least two polymer precursors, 
 wherein each polymer precursor comprises azobenzene as said photoresponsive moiety, flanked by alkyl chains having from 4 to 10 carbons, and 
 wherein the surfactant and at least one of the at least two polymer precursors comprise a crosslinking moiety selected from the group consisting of acrylate, vinyl ether, and epoxide. 
 
     
     
       2. The method of  claim 1 , wherein each polymer precursor further comprises a backbone-forming moiety selected from the group consisting of acrylate, norbornene, and siloxane. 
     
     
       3. The method of  claim 1 , wherein said at least two polymer precursors are 
       
         
           
           
               
               
           
         
       
       and 
       
         
           
           
               
               
           
         
       
       and said surfactant is 
       
         
           
           
               
               
           
         
       
     
     
       4. The method of  claim 1 , wherein said photoresponsive particle actuator is an oblate spheroid with a size of from 50 nanometers to one micron. 
     
     
       5. The method of  claim 1 , wherein said photoresponsive particle actuator is configured to:
 (a) open and close a microfluidic channel; 
 (b) actuate a MEMS device; 
 (c) open and close a compartment; or 
 (d) a combination of the above. 
 
     
     
       6. The method of  claim 1 , wherein, when said photoresponsive particle actuator is expanded, the actuator experiences at least about a 20% increase in said at least one dimension as compared to when the actuator is contracted. 
     
     
       7. The method of  claim 1 , wherein said irradiating with ultraviolet light and/or irradiating with visible light comprises irradiating with an intensity of at least 0.15 mW/cm 2 . 
     
     
       8. The method of  claim 1 , wherein said surfactant comprises a carboxylate, sulfonate, imidazole, or amine group.